1. Technical Field
The embodiments described herein relate to a semiconductor integrated circuit, and more particularly, to an apparatus for supplying an overdriving signal in a semiconductor integrated circuit.
2. Related Art
Many conventional semiconductor memory apparatus, including Dynamic Random Access Memory (DRAM) apparatus, use cross coupled sense amplifiers. When a voltage applied to the sense amplifier reaches a threshold voltage (VT) level, the sensing speed considerably decreases, which can have an adverse effect. In order to solve the problem, an overdriving scheme is used, where the sense amplifier receives a voltage Vcore as a driving voltage, and an external voltage VDD as an overdriving voltage.
As shown in FIG. 1, a conventional overdriving signal supplying apparatus includes first to third NMOS transistors NM1, NM2, and NM3, a sense amplifier 2000, and a pre-charging unit 3000.
The first to third NMOS transistors NM1 to NM3 respectively receive first to third sense amplifier control signals (SAP1), (SAP2), and (SAN) and supply to the sense amplifier 2000 the external voltage VDD, the core voltage Vcore, and a ground voltage VSS, respectively. The precharging unit 3000 supplies a pre-charge voltage Vblp to the sense amplifier 2000 in a precharge mode.
As shown in FIG. 2, in the overdriving signal supplying apparatus, when a word line WL is enabled and then the third sense amplifier control signal (SAN) is enabled, the ground voltage VSS is supplied to the sense amplifier 2000. Then, the first sense amplifier control signal (SAP1) is enabled for a predetermined time to overdrive sense amplifier 2000, causing the external voltage VDD to be supplied to the sense amplifier 2000. Therefore, amplification by the sense amplifier 2000 can be rapidly performed. Subsequently, the second sense amplifier control signal (SAP2) is enabled, and the first sense amplifier control signal (SAP1) is disabled, so that the core voltage Vcore is supplied to the sense amplifier 2000. In this way, a pair of bit lines of the sense amplifier 2000 reach the core voltage Vcore and the ground voltage VSS, respectively.
However, it is difficult to maintain the overdriving voltage at a fixed value due to the external voltage VDD. That is, the threshold voltage and current of transistors included in the sense amplifier 2000 change according to the external voltage VDD. Therefore, when the external voltage VDD is low, the overdriving voltage may be low, and when the external voltage VDD is high, excessive overdriving may occur. As a result, when the overdriving voltage is lower, a sensing margin of the sense amplifier 2000 is reduced, which may cause a malfunction. Simply increasing the overdriving voltage can cause the sensitivity of the sense amplifier 2000 to be lowered and power consumption to increase. Also, when the external voltage VDD exhibits significant noise, the reliability and sensitivity of a sense amplifier are considerably lowered.